Assembly of printed circuit boards

ABSTRACT

A printed circuit board (PCB) assembly includes a first PCB and a second PCB disposed substantially parallel and opposite to each other, such that a second side of the first PCB is opposite to a first side of the second PCB; wherein the second PCB has a first set of side connectors on its first side and a second set of side connectors on its second side, configured for both electrical power supply to and signal communication with the second PCB; the second PCB both electrically and mechanically connected to the second side of the first PCB via a first elastomeric connector; and the second PCB electrically connected to the first PCB via its second set of side connectors and a flexible electrical connector that is electrically connected to the second set of side connectors and the first PCB.

FOREIGN PRIORITY

This application claims priority to Great Britain Patent Application No.1409416.3, filed May 28, 2014, and all the benefits accruing therefromunder 35 U.S.C. §119, the contents of which in its entirety are hereinincorporated by reference.

BACKGROUND

The invention relates in general to the field assemblies of printedcircuit boards (or PCBs). In particular, it is directed to assemblies ofstorage module PCB and mSATA or SATA M.2 PCBs.

A microserver is a server class computer which is based on a system on achip (SoC). An example of microserver is discussed in Doering, A. C.;Kiss, T., “Monitoring and Controlling System for Microservers,” Paralleland Distributed Processing Symposium Workshops & PhD Forum (IPDPSW),2013 IEEE 27th International, pp. 1538-1541, May 2013,http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6651048&isnumber=6650854.

Microservers may use various types of modules, for example: computemodules (e.g., using a DIMM-240 connector); power converter modules(using an extreme PowerEdge connector) and switch modules (using anImpact 100 series connector, Molex). While the main purpose of thecompute modules is to contain processors and main memory, one maycontemplate using them together with storage devices, for instance basedon Flash technology. However, doing so poses several problems ofconnections and, in turn, of encumbrance. This can become a seriousissue in space-constraint arrangements as needed in microservers.

SUMMARY

In one embodiment, a printed circuit board (PCB) assembly includes afirst PCB and a second PCB disposed substantially parallel and oppositeto each other and each having a first side and a second side opposite toeach other, such that the second side of the first PCB is opposite tothe first side of the second PCB; wherein the second PCB has a first setof side connectors on its first side and a second set of side connectorson its second side, the first and second sets of connectors configuredfor both electrical power supply to and signal communication with thesecond PCB; the second PCB both electrically and mechanically connectedto the second side of the first PCB via a first elastomeric connectorarranged between the first side of the second PCB, where it connects tothe first set of connectors, and the second side of the first PCB; andthe second PCB electrically connected to the first PCB via its secondset of side connectors and a flexible electrical connector that iselectrically connected to the second set of side connectors and thefirst PCB.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a 2D cross-sectional view of a simplified representation of aone-sided assembly, i.e., comprising one or more second PCBs arranged onone side of a first PCB, according to embodiments;

FIG. 2 is a 2D cross-sectional view of a simplified representation of atwo-sided assembly, i.e., comprising one or more second PCBs arranged oneach side of the first PCB, according to embodiments;

FIG. 3 illustrates a variant to FIG. 2, where a flexible electricalconnector used to connect the first and second PCBs is in a U-turnconfiguration, according to embodiments;

FIG. 4 is a 2D (top) view of a simplified representation of assembliessuch as depicted in FIGS. 1-3, and according to embodiments; and

FIG. 5 is a cross-section view of a simplified representation of a flexconnector, as involved in embodiments of the invention.

DETAILED DESCRIPTION

According to a first aspect, an assembly of printed circuit boards orPCBs, includes a first PCB and a second PCB maintained essentiallyparallel and opposite to each other and having, each, a first side and asecond side opposite to each other, such that the second side of thefirst PCB is opposite to the first side of the second PCB, wherein thesecond PCB: has a first set of side connectors on its first side and asecond set of side connectors on its second side, the first and secondsets of connectors configured for both electrical power supply to andsignal communication to and/or from the second PCB; is both electricallyand mechanically connected to the second side of the first PCB via afirst elastomeric connector arranged between: the first side of thesecond PCB, where it connects to the first set of connectors, and thesecond side of the first PCB; and is electrically connected to the firstPCB via: its second set of side connectors and a flexible electricalconnector that is electrically connected to the second set of sideconnectors and the first PCB.

In embodiments, the second PCB is electrically connected to the firstPCB via: a second elastomeric connector, which connects to the secondset of side connectors of the second PCB; and the electrical connector,which connects both: the second elastomeric connector; and the firstPCB.

The second PCB is electrically connected to the first side of the firstPCB via: its second set of side connectors and the flexible electricalconnector, the latter connected to the first side of the first PCB.

The electrical connector has a portion extending over a lateral edge ofthe first PCB and a lateral edge of the second PCB, perpendicularly tothe average planes of the first and second PCBs. The electricalconnector is a flat flex cable.

In embodiments, the electrical connector is a rigid-flex connector,which is integral with the first PCB.

The above assembly further includes a fastening structure maintainingthe flex connector, the first elastomeric connector, the secondelastomeric connector, as well as a lateral edge of each of the firstPCB and the second PCB.

The fastening structure has a U-section and is arranged such as to clampthe flex connector, the first elastomeric connector, the secondelastomeric connector, and the lateral edge of each of the first PCB andthe second PCB.

The assembly includes a set of at least two, preferably four and morepreferably eight second PCBs, each configured with respect to the firstPCBs similarly as the second PCB, whereby each of the second PCBs ismaintained essentially parallel and opposite to the first PCB, andwherein, the second PCBs are arranged side by side on one side of thefirst PCB or in one or more pairs, with each second PCBs of one pair oneach side of the first PCB.

In embodiments, one or more of the second PCBs of the set are arrangedon the second side of the first PCB, and one or more other second PCBsof the set are arranged on the first side of the first PCB.

The assembly includes a set of four second PCBs, each arranged on thesecond side of the first PCB, and wherein, preferably, the assemblycomprises a set of eight second PCBs, wherein four second PCBs of theset are arranged on the first side of the first PCB and four second PCBsof the set are arranged on the second side of the first PCB.

In embodiments, the first PCB includes a storage module PCB and anysecond PCB comprises an mSATA PCB.

The above assembly further comprises an essentially flat flash memorycomponent on one side of a second PCB, which flash memory component hasan average thickness that substantially corresponds to the thickness ofthe first elastomeric connector, and wherein, preferably, the assemblyfurther comprises two flash memory components on each side of the secondPCB, and wherein, more preferably, one or each flash memory component isa NAND flash memory.

In embodiments, this assembly further includes a power converter and amodule controller, each arranged in electrical contact with, preferablyon one side of, the first PCB, wherein the module controller iselectrically connected to one or more second PCB and is otherwiseconfigured to enable the power converter.

The first elastomeric connector, and other elastomeric connectors of theassembly, are each electrically conducting along directionsperpendicular to its average plane and are not electrically conductingin-plane, and each include deformable layers of alternating conductiveand insulating materials.

Devices embodying the present invention and fabrication methods thereofwill now be described, by way of non-limiting examples, and in referenceto the accompanying drawings. Technical features depicted in thedrawings are not necessarily to scale.

Embodiments of the invention are first generally described in referenceto FIGS. 1-4. Embodiments described herein provide an assembly 10 ofprinted circuit boards (hereafter PCBs, for short), wherein the assemblyincludes two types of PCBs: a first PCB 21 and a second PCB 22, whichare maintained essentially parallel and opposite to each other (they areessentially flat components, as known). Each of the PCBs has a first(main) side and a second (main) side, which are opposite to each other.For instance, and as depicted in the appended drawings, the first PCB 21has a first side 211 opposite to its second side 212. Similarly, thesecond PCB 22 has opposite first and second sides 221 and 222, such thatthe second side 212 of the first PCB 21 is opposite to the first side221 of the second PCB 22. Note that, in FIG. 1, the “first side” of anyPCB (21 or 22) is always on the left and the second side is always onthe right.

The second PCB 22 has a first set C1 of side connectors on its firstside 221 and a second set C2 of side connectors on its second side 222.The first and second sets of connectors are known per se. They can beused for both electrical power supply and signal communication. Inparticular, they are configured for enabling electrical power supply tothe second PCB and signal communication to and/or from the second PCB.

Furthermore, the second PCB 22 is both electrically and mechanicallyconnected to the second side 212 of the first PCB 21 via a firstelastomeric connector 31. The latter is arranged between: the first side221 of the second PCB, where it connects to the first set C1 ofconnectors; and the second side 212 of the first PCB, e.g., via contacttracks 45.

Finally, the second PCB 22 is electrically connected to the first PCB 21via: its second set C2 of side connectors and a flexible electricalconnector 40. The flexible electrical connector 40 is electricallyconnected to each of: the second set C2 of side connectors; and thefirst PCB.

As further discussed in more detail later, the first PCB typically is astorage module PCB (e.g., 1.27 mm thick, for DIMM socket), whereas thesecond PCB may for example be an mSATA or a SATA M.2 PCB, i.e., atwo-sided or double-sided connected PCB, which may include flashmemories 61, 62 on each of its first and second sides. The first andsecond PCBs extend generally in parallel planes. As known in the art,mSATA stands for mini-SATA, i.e., a standard used by small devices suchas 1.8″ SATA drives and mini SSDs. SATA or Serial ATA stands for SerialAdvanced Technology Attachment.

The side connectors C1, C2 of the second PCB 22 are edge connectors. Asknown, an edge connector is a part of a PCB that can be plugged into acomputerized device. It generally involves a row of broad metallictracks that provide electrical connection. The invention neverthelessextends, in principle, to PCBs having any type of connectors (for signalcommunication and/or power supply) on opposite sides.

The flexible electrical connector 40 is typically what is usually calleda flex connector, e.g., a flex flat cable. The connector 40 may connectto the first PCB 21, e.g., on its first side, via a solder joint 80. Theversatility of a flexible electrical connector allows for minimizationof the space needed for connecting the second set C2 of connectors tothe first PCB. Indeed, the conventionally available connectors, e.g.Molex 48338-0090 or MMT MiniPCIE600, are too large, in height and depth,for achieving compact arrangements. On the contrary, the PCB assembliesproposed herein allow for instance to fit four mSATA drives on one sideof a microserver compute module of 138×55 mm (including DIMM contacts),which would not be possible when using conventional connectors.

The flexible electrical connector 40 is preferably a separate component,i.e., not integral with either the first or the second PCB. It is bothelectrically and mechanically connected to each of the first PCB and thesecond PCB, via the second side 222 of the second PCB 22.

For instance, FIG. 5 shows a cross-section view of a simplifiedrepresentation of an example of flex connector that can be used inembodiments of the present invention. This view shows a flex 40,comprising copper tracks (for conducting electrical current and therebysignal) 46, 47. The two copper tracks are separated by a thick innermaterial 43 (typically a polymer providing the mechanical properties ofthe flex 40 and ensuring electrical insulation between the tracks 46,47), which typically has a controlled thickness. The external insulatingmaterial 41, 42 (typically a polymer too) has typically a minimalthickness. This material is open on selected areas (not insulated) toprovide contact areas 44, 45. Note that flexes may be provided withnon-insulating areas 44, 45 on a same side (e.g., when implemented inembodiments such as depicted in FIG. 1 and FIG. 2) or on opposite sides(e.g., when implemented in embodiments such as depicted in FIG. 3). Inthis respect, there are techniques that allow ‘soldering’ from bothsides, either by having a second layer and vias on non-insulating areaor by having an opening in the inner material 43. Finally, numerousvariants to FIG. 5 can be contemplated. The example of FIG.5 isparticularly well suited for high-speed SATA using a double layer flexto work in an impedance controlled manner.

In variants, the flexible connector 40 may be a so-called rigid-flex,i.e., integral with the first PCB. In such cases, the flex is acontinuation of the first PCB (it is part of, or integral therewith),and is mechanically and electrically connected to the other PCB. Byelectrical connection, it is meant a connection that allows for powersupply and/or signal transmission. The flexible electrical connector canaccordingly be used for electrical power and/or signal supply.

Finally, the use of an “elastomeric connector” 31 allows fortransmitting signal/power perpendicularly to the metallic tracks or pinsof the connectors C1. The term “elastomeric connector” is known in theart to refer to an element that is electrically conducting in some(e.g., perpendicularly to its average plane) but not all (e.g.,in-plane) directions, which is appropriate in the present case becauseit allows for compactness and further eases the connection with the sideconnectors C1. The elastomeric connectors 31, 32 may for instancecomprise slightly deformable layers (e.g., rubberized layers) ofalternating conductive and insulating materials. Consistently, the term“elastomeric connector” is meant to describe any elastic material thatresumes its original shape when a deforming force is removed, and whichis electrically conducting along directions perpendicular to the averageplanes of the first and second PCBs, and which are not electricallyconducting along directions parallel to the average planes of the PCBs.Preferably, such connectors are, each, made of deformable layers ofalternating conductive and insulating materials. The elastomericconnectors used herein shall preferably have an aspect ratio (theirthickness is less than their width, to optimize compactness), such as tobe electrically conducting along directions perpendicular to theiraverage planes (but not electrically conducting in-plane).

Elastomeric connectors are usually used in shock and anti-vibrationapplications. They can occasionally be used to create a gasket-likeseal. Here, the elastomeric connector 31 is used to leverage itsdirectional conductivity, which provides a shortest path to the firstPCB 21, whereas the flexible connector 40 on the opposite side allows tooptimally get around the edge of the PCB 22. Altogether, this allows forobtaining very compact arrangements, as illustrated in the embodimentsshown in FIGS. 1-3.

Elastomeric connectors used in the present applications may preferablycomprise deformable layers of alternating conductive and insulatingmaterials. They are typically chosen to have a height or thicknessmatching substantially the height or thickness of the flat Flash memorycomponents 61, 62 of the second PCB 22, to further improve the resultingcompactness.

Using a flexible electrical connector 40, e.g., a flex connector or aflex flat cable, is in fact advantageous in many respects. It can bebent such that the resulting encumbrance will essentially be determinedby the thickness of the stack of connectors 31-32, i.e. the sum of thethickness of the connectors 31 and 22, as illustrated in FIGS. 1-3.Different configurations of the flex 40 are possible (compare FIGS. 1, 2and 3, a U-turn configuration may be preferred, to further improvecompactness, see FIG. 3). When one desires to use different PCB (e.g.,mSATA drives) 22, each connected to the first PCB 21, side by side or onopposite sides thereof, there can be tolerances in the height of thecomponents which determine the distance between PCBs 21 and 22. Theelastomeric connector 40 is elastic and deformable, so that itsthickness can be somewhat adapted to conform to particular heightconstraints.

To summarize, the above arrangements allow for compact structures to beobtained, notably in terms of height (i.e., the horizontal direction inFIGS. 1-3). Ideally, only the thickness of the flexible electricalconnector 40 is added to the heights of the PCBs and possibly the flashmemories 61, 62. In practice, a little bit more than the flex thicknessis added, due to its bending radius. Eventually, the obtained structuresare more compact in each dimension.

The above arrangements advantageously apply to storage modules. Assume,for instance, that one wants to place, e.g., four or eight mSATA modules22 (depending on the height profile of neighbor modules) on the carrierPCB 21. One problem that arises is the size of connectors between themSATA modules and the carrier PCB. The conventionally availableconnectors are too large, in height and depth to meet the requirements,e.g., to fit four mSATA modules on one side of the compute moduleincluding DIMM contacts. This problem can be solved, thanks to theinvention, by connecting the mSATA modules via the elastomericconnectors 31 on one side and flexible connectors 40 on the other side,which both contact the carrier PCB 21, as described above in referenceto FIGS. 1-3.

Next, in embodiments such as illustrated in FIGS. 1-3, the second PCB 22is electrically connected to the first PCB 21 via: a second elastomericconnector 32, which connects to the second set C2 of side connectors ofthe second PCB 22; and the electrical connector 40 (the latter connectsboth the second elastomeric connector 32 and the first PCB). Sinceelastomeric connectors advantageously provide a satisfactory contactpressure on the side connectors C1 and C2, an additional elastomericconnector 32 is preferably used on the side opposite to the side wherethe first elastomeric connector 31 is arranged. The second elastomericconnector 32 connects the second set C2 of connectors to the flexibleconnector 40, which ensures sufficient contact pressure for connectingboth the second set C2 of connectors and the flex 40. This, in turn,allows to reliably connect the second PCB 22 to the first PCB 21. Inother words, using a second elastomeric connector makes the contactbetween, on the one hand, the first PCB and the second PCB and, on theother hand, the flex 40 and the second PCB 22, more reliable.

The use of the second elastomeric connector 32 further eases theconnection of the flexible connector 40, as the later does not need tobe connected to the connector 32 by its very end. On the contrary, anend piece of the flex 40 is typically dangling, as illustrated in FIGS.1-3.

The flex connector 40 is fully isolated but in contact areas 44, 45 (seeFIG. 5), i.e., the contact areas to the elastomeric connector 32, 32 aand to the first PCB 21. At the contact locations to the elastomericconnector, the non-isolated contact areas 44, 45 preferably match theform, size and arrangement of the contact areas on the second PCB 22. Inorder to ease the assembly, the contact areas on the flex connector canbe made slightly narrower than the standard contact pads, for instancethe mSATA standard.

Electrical contact is established by pressing the flex connector againstthe elastomeric connector. The reliability of such a connection will besubstantially improved by way of mechanical pressure. Mechanicalpressure can for instance be achieved by a fastening structure 50 asdescribed later. There are, however, other ways to create that pressureor maintain the flex 40. For example, the whole assembled module couldbe casted in resin, it could be packed air-tight in strong foil and airsucked out (to create an underpressure within the foil), several similarmodules can be packed close together so that the neighboring modulespress against the assembly, or if the module is used in a pre-formedenclosure such as for a mobile phone or tablet computer the enclosurewould provide the fixing pressure.

The flex 40 may be soldered directly to the PCB 21 on one side, e.g.,via pads 80, and will contact the other PCB 22 via the elastomericconnector 32, 32 a. Geometrically speaking, the electrical connector 40connects a second side 322 of the second elastomeric connector 32 i.e.,the right-most side in FIG. 1, where this second side 322 is opposite toa first side of the second elastomeric connector 32 i.e., the left-mostside of connector 32 in FIG. 1 (not referenced for clarity). Since thesecond elastomeric connector 32 is on the second side 222 of the secondPCB 22, the first side of the second elastomeric connector 32 typicallyfaces the second side 222 of the second PCB 22.

Referring now more specifically to FIG. 1, the second PCB 22 may, inembodiments, be electrically connected to the first side 211 of thefirst PCB 21. This connection involves its second set C2 of sideconnectors and the flexible electrical connector 40. The secondelastomeric connector 32 still connects the second set C2 of connectorsto the flexible connector 40. Use is made of the flexibility of theflexible connector 40 to connect the first side 211 of the first PCB 21,as depicted in FIG. 1.

As further seen in FIG. 1, the electrical connector 40 may have aportion extending over the lateral edge of the first PCB 21 and thelateral edge of the second PCB 22, perpendicularly to the average planesof the first and second PCBs, such as to get around the first PCB andconnect to its first side 211.

In variants, the flexible electrical connector 40 may simply connect tothe second side 212 of the first PCB 21, as depicted in FIGS. 2 and 3,e.g., using again appropriate contact pads (80). In that case, theelectrical connector 40 typically has a middle portion extending overlateral edges of the second PCB 22 and elastomeric connectors 31, 32.

Connecting the flex 40 to the first PCB 21 on its second side 212 easesthe alignment; it is further beneficial in that no stress is applied tothe flex on the left edge of the first PCB 21. Accordingly, the flexconnector 40 may also connect to the second side 212 of the first PCB21.

As described earlier, the electrical connector 40 is preferably a flatflex cable, which is known per se. In the present context, it allows forminimizing the overall encumbrance of the connections. In variants, theelectrical connector may be a rigid-flex connector, which is integralwith the first PCB 21. In that case, the rigid-flex connector is anextension of the first PCB 21 and solely needs to be connected to thesecond PCB 22 (no additional mechanical connection is needed between therigid-flex and the first PCB 21).

Advantageously, the present assemblies may further comprise a fasteningstructure 50 (or any suitable binding structure), arranged such as tomaintain the flex connector 40, the first and second elastomericconnectors 31, 32, as well as a lateral edge of each of the first PCB 21and the second PCB 22. Such a fastening structure 50 provides mechanicalpressure to maintain the needed electrical and mechanical connectionsbetween the various components above, in a particularly reliable manner.

As depicted in FIGS. 1-3, this fastening structure 50 has a U-sectionand is arranged such as to clamp the flex connector 40, the first andsecond elastomeric connectors 31, 32, and the lateral edge of each ofthe first PCB 21 and the second PCB 22. The fastening structure may be aholder, a fastener like a binder clip or a clamp, having typically aU-section. It allows for fastening and compressing the superimposed PCBsby compressing the deformable elastomeric connectors 31, 32, therebyreducing the height of the assembly and improving compactness. Suchfastening structures further have minimal encumbrance.

Referring now to FIGS. 1-4 (and in particular to FIG. 4), inembodiments, the assembly shall typically comprise a set of severalsecond PCBs, as made possible thanks to the compact arrangementsproposed herein. The assembly may for instance comprise a set of four oreight second PCBs 22. Each of these second PCBs is arranged with respectto the first PCBs similarly as discussed above. Namely, each second PCBis maintained essentially parallel and opposite to the first PCB andconnected to the first PCB by way of elastomeric connectors and flexibleconnectors.

The second PCBs may for instance be arranged side by side on one side ofthe first PCB, as illustrated in FIG. 4. The second PCBs may also bearranged in one or more pairs, with each second PCBs of one pair on eachside 211, 212 of the first PCB, as illustrated in FIGS. 2 and 3. As seenin these figures, two second PCBs are maintained essentially paralleland opposite to the first PCB and connected to the first PCB by way ofelastomeric connectors 31, 32, 31 a and 32 a, and flexible connectors40, 40 a. In addition, connectors C1, C2, C1 a, C2 a and contact tracks45 may be involved, just as before. This way, very compact arrangementsof PCBs can be achieved.

An example of compact arrangement is one where the assembly comprises aset of four second PCBs 22 arranged on one side 212 of the first PCB 21,as seen in FIG. 4. Symmetrizing this configuration, one obtains a set ofeight second PCBs 22, with four second PCBs arranged on one side 211 ofthe first PCB 21 and four second PCBs arranged on the other side 212 ofthe first PCB 21. Still, less symmetrical arrangements may becontemplated, with one or more second PCBs arranged on one side 212 ofthe first PCB 21, and possibly one or more other second PCBs arranged onthe other side 211 of the first PCB 21. The optimal configuration may ineach case depend on other components present in the assembly.

Such arrangements are compatible with second PCBs comprising, each, oneor two flat flash memory components 61, 62 on one side (or oppositesides) thereof, e.g., a NAND flash memory components. More generally,one or more of, or each of the second PCBs 22, 22 a evoked herein maycomprise flat flash memory components 61, 62, 61 a, 62 a. Suchcomponents can for instance be soldered to both sides of a second PCB.Note that one or more, or each of the second PCBs may actually comprisemore than two flat flash memory components, e.g., with two or morecomponents provided on one same side thereof. Advantageously, theaverage thickness of an elastomeric connector 31, 32 may be chosen ordesigned such as to substantially amount to that of a flash memorycomponent 61, 62. For example, any or each second PCB may be an mSATAPCB, which comprises two flash memory components 61, 62 on each sidethereof, which preferably are NAND Flash memory components. As furtherillustrated in FIGS. 1-3, one 62 of the flash memory components may beprovided with a recess accommodating fixation means 71. Additional,corresponding memory controllers may be provided too, if necessary.

As said earlier, the optimal configuration of the second PCBs mayfurther depend on other components present in the assembly. In thisrespect, the present PCB assemblies may further comprise a powerconverter 80 and a module controller 90, as illustrated in FIG. 4. Theseadditional modules 80, 90 are preferably arranged on one side of thefirst PCB 21 and are, each, arranged in electrical contact with thefirst PCB 21. The module controller is typically electrically connectedto one or more second PCB 22 and is otherwise configured to enable thepower converter 80.

Present PCB assemblies are preferably used in micro servers, to whichthe present invention extends. As known, a microserver is a small serverappliance that essentially works like a server, designed for ease ofinstallation and maintenance. It typically comes with an operatingsystem, hardware and software preinstalled and configured by themanufacturer, although some configuration functions shall still beperformed by the end-user. In variants, the methods and arrangementsdescribed herein can be used in the fabrication of integrated circuitchips packages, as part of either an intermediate product or an endproduct, where this end product may be any product that includesintegrated circuit chips, ranging from low-end applications to advancedcomputer products.

The above embodiments have been succinctly described in reference to theaccompanying drawings and may accommodate a number of variants. Severalcombinations of the above features may be contemplated. Examples aregiven in the next section.

The PCB assemblies discussed above are preferably implemented in amicroserver that consists of three module types: compute modules (usinga DIMM-240 connector); power converter modules (using an extremePowerEdge connector); and switch modules (using an Impact 100 seriesconnector, Molex). As noted earlier, the compute modules can also beused with storage devices, for instance based on Flash technology, e.g.,mSATA disks. The mSATA disk standard measures 50.8×30 mm. The computemodule height is 55 mm, its width is 138 mm (including the DIMMcontacts) and its thickness is 1.27 mm. In the preferred microserversthe pitch from one compute module to the next is 7.6 mm. Preferably, thestorage module holds four or eight mSATA disks depending on the heightprofile of neighbor modules. As explained in the previous section,present embodiments allow to overcome issues arising from the size andencumbrance of usual connectors between the mSATA modules and thecarrier PCB, and therefore allow to fit four mSATA drives on one side ofthe microserver compute module (of 138×55 mm, including DIMM contacts),or two sets of four mSATA drives on each side. Amongst other examples,SATA M.2. disks (under NGFF standard) can be contemplated too, insteadof the mSATA disks. Still, mSATA disks are hereafter assumed, for thesake of illustration.

In all cases, a combination of elastomeric connectors (e.g., availableunder the trade name ZEBRA), flexible connectors and a stiff (e.g.metallic or ceramic) U-shaped holder are used for contacting the mSATAmodules. The mSATA modules are otherwise fixed to the main PCB by way ofbolts and nuts 71, as illustrated in FIGS. 1-3 (FIG. 3 differs in theform of the flexible connector, here making a U-turn). FIG. 4 shows thefront side of an entire module, including two optional components 80, 90for power conversion and module control. Useful details concerning suchcomponents can be found in the publication “Monitoring and ControllingSystem for Microservers,” cited in introduction.

The flexible connectors are not visible in FIG. 4. Advantageously, theyshould consist of two segments per mSATA disk, because the mSATAconnector is split between power and signals. By splitting the flexibleconnectors, one can use different technologies for the two cases, aone-layer version with thicker copper layer for the power supply and adual layer for controlled impedance for the high-speed signals. Moregenerally, any flexible connector 40 used in this invention could besplit between power and signals, such as to exhibit distinct channels toconvey power and signal.

The present assemblies can be obtained using any suitable fabricationmethod. Advantageously yet, a tool may be designed for assembly of themodules, which:

1. Holds the first PCB 21 firmly at a precisely fixed location (withe.g., a deviation less than 0.1 mm);

2. Avoids bending of the first PCB 21;

3. Allows aligning the second PCBs 22 individually on first PCB 21; andafterwards allows to:

4. Hold the second PCBs 22 in their positions;

5. Insert the inner elastomeric connector(s) 31;

6. Hold the inner elastomeric connector(s) 31 at its location;

7. Add the outer elastomeric connector 32;

8. Hold the outer elastomeric connector 32, while

9. Aligning the flexible connectors 40 with the second PCB; and finally

10. Adding the fastening structure 50

The above process assumes that the flex print 40 is already attached tothe first PCB. A tool enabling this process can be made either formanual assembly or automated volume assembly, and can be scaled for costvs. productivity.

Item 1 above can be achieved with a rubber covered wrench. Item 2 can beachieved by applying tension to both sides of the base PCB, or for theone-sided case by support from the back side over the entire area. Item3 can done with two blades that are hold in a parallel fashion at adistance corresponding to the width of the disks (e.g., 30 mm for mSATAdisks), similar to a tweezers. For more precision and faster operation aguidance trail per disk can be provided, which has a fixed locationrelative to the PCB fixture of item 1. Item 4 can be achieved with apunch that presses the disks (preferably at two points) against the basePCB. It can be further improved by applying a gel or paste between thedisk and storage module PCB. Item 6 can be achieved with a narrow barthat is arranged from top. Item 8 can be carried out with a comb-likestructure that presses the outer elastomeric connector between thelocations of the flex connectors. The end of the flex prints can befixed by a set of small tongs during addition of the holder. Allalignment operations can be improved by means of magnifying glasses,cameras, and/or transparent templates.

While the present invention has been described with reference to alimited number of embodiments, variants and the accompanying drawings,it will be understood by those skilled in the art that various changesmay be made and equivalents may be substituted without departing fromthe scope of the present invention. In particular, a feature recited ina given embodiment, variant or shown in a drawing may be combined withor replace another feature in another embodiment, variant or drawing,without departing from the scope of the present invention. Variouscombinations of the features described in respect of any of the aboveembodiments or variants may accordingly be contemplated, that remainwithin the scope of the appended claims. In addition, many minormodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiments disclosed, but that the present inventionwill include all embodiments falling within the scope of the appendedclaims. In addition, many other variants than explicitly touched abovecan be contemplated. For example, other storage modules than thosespecifically discussed here can be contemplated.

1. A printed circuit board (PCB) assembly, comprising: a first PCB and asecond PCB disposed substantially parallel and opposite to each otherand each having a first side and a second side opposite to each other,such that the second side of the first PCB is opposite to the first sideof the second PCB; wherein the second PCB has a first set of sideconnectors on its first side and a second set of side connectors on itssecond side, the first and second sets of connectors configured for bothelectrical power supply to and signal communication with the second PCB;the second PCB both electrically and mechanically connected to thesecond side of the first PCB via a first elastomeric connector arrangedbetween the first side of the second PCB, where it connects to the firstset of connectors, and the second side of the first PCB; and the secondPCB electrically connected to the first PCB via its second set of sideconnectors and a flexible electrical connector that is electricallyconnected to the second set of side connectors and the first PCB.
 2. Theassembly of claim 1, wherein the second PCB is electrically connected tothe first PCB via a second elastomeric connector, which connects to thesecond set of side connectors of the second PCB, and the electricalconnector, which connects both the second elastomeric connector and thefirst PCB.
 3. The assembly of claim 2, wherein the second PCB iselectrically connected to the first side of the first PCB via its secondset of side connectors and the flexible electrical connector, the latterconnected to the first side of the first PCB.
 4. The assembly of claim1, wherein the electrical connector has a portion extending over alateral edge of the first PCB and a lateral edge of the second PCB,perpendicularly to the average planes of the first and second PCBs. 5.The assembly of claim 4, wherein the electrical connector is a flat flexcable.
 6. The assembly of claim 4, wherein the electrical connector is arigid-flex connector, which is integral with the first PCB.
 7. Theassembly of claim 1, further comprising a fastening structuremaintaining the flex connector, the first elastomeric connector, thesecond elastomeric connector, and a lateral edge of each of the firstPCB and the second PCB.
 8. The assembly of claim 7, wherein thefastening structure has a U-section and is arranged so as to clamp theflex connector, the first elastomeric connector, the second elastomericconnector, and the lateral edge of each of the first PCB and the secondPCB.
 9. The assembly of claim 1, wherein the assembly comprises a set ofat least two second PCBs, each configured with respect to the first PCBssimilarly as the second PCB, wherein each of the second PCBs ismaintained substantially parallel and opposite to the first PCB, andwherein the second PCBs are arranged side by side on one side of thefirst PCB or in one or more pairs, with each second PCBs of one pair oneach side of the first PCB.
 10. The assembly of claim 9, wherein one ormore of the second PCBs of the set are arranged on the second side ofthe first PCB, and one or more other second PCBs of the set are arrangedon the first side of the first PCB.
 11. The assembly of claim 9, whereinthe assembly comprises a set of four second PCBs, each arranged on thesecond side of the first PCB, wherein four second PCBs of the set arearranged on the first side of the first PCB and four second PCBs of theset are arranged on the second side of the first PCB.
 12. The assemblyof claim 1, wherein the first PCB comprises a storage module PCB and anysecond PCB comprises an mSATA PCB.
 13. The assembly of claim 1, furthercomprising a substantially flat flash memory component on one side of asecond PCB, which flash memory component has an average thickness thatsubstantially corresponds to the thickness of the first elastomericconnector, and wherein the assembly further comprises two flash memorycomponents on each side of the second PCB, and wherein one or each flashmemory component is a NAND flash memory.
 14. The assembly of claim 1,further comprising a power converter and a module controller, eacharranged in electrical contact with, on one side of, the first PCB,wherein the module controller is electrically connected to one or moresecond PCB and is otherwise configured to enable the power converter.15. The assembly of claim 1, wherein the first elastomeric connector iselectrically conducting along directions perpendicular to its averageplane and are not electrically conducting in-plane, and comprisedeformable layers of alternating conductive and insulating materials.